1. Field of the Invention
The present invention relates to a semiconductor memory device (hereinafter "memory"), more particularly to a memory of a static random access memory (S.RAM) type composed of emitter-coupled-logic (ECL) memory cells.
Various types of memories have been developed and put into practical use. Recent research and development has concentrated in achieving greater miniaturization of memory patterns, i.e., increasingly higher densities of packaging of integrated circuit (IC) memories. To fabricate a denser IC memory, however, it is not sufficient merely to miniaturize the memory cells and wiring. Miniaturization creates additional problems which themselves must be solved.
2. Description of the Prior Art
In a prior art ECL-type S.RAM, increased miniaturization and higher integration create the problem of electromigration. More specifically, when the current density of, for example, aluminum wiring exceeds a predetermined threshold level, since the aluminum wiring is made narrower in width upon miniaturization, the aluminum in a solid state is transformed by heat into a molten state and will flow elsewhere.
When electromigration takes place, the desired memory function cannot be guaranteed. Therefore, excessive current density must be prevented, not only for aluminum wiring but all other wiring of other conductive materials, to suppress electromigration.